I suppose I might be in the opposite myself, as the Oberth hull seems to be one of the few that looks specifically modular and also cheap to produce. I can easily see where it would have led to a number of different variants that could perform specific missions.

Unfortunately, we never actually saw any such modularity whenever we saw an Oberth on screen

Now I have seen fan-made models of the Oberth with such things as large cargo containers or a medical-based secondary hull in place of the regular secondary hull, so I can see your point. But even when an Oberth was specifically referenced to be a supply ship (the Biko), it had the same hull as it always has.